Process of making surface alloyed



Patented Jan. 31, 1939 PATENT OFFICE PROCESS OF MAKING SURFACE ALLOYEDMATERIALS Hugh S. Cooper, Cleveland Heights, Ohio, as-

signor to Cooper Products, Inc., Cleveland, Ohio, a corporation of OhioNo Drawing. Application May 9, 1936,

' Serial No. 78,895

4 Claims.

The present invention relates to surface alloyed materials, and tomethods of producing the same. More particularly the invention relatesto a process of producing materials upon which a surface 5 alloy hasbeen formed by cementation, especially ferrous materials having asurface alloy of ferro chrome produced thereon by cementation, whichprocess includes subjecting the same to both hot and cold metal workingoperations.

An object of the invention is the provision of a. novel method ofproducing surface alloyed materials, especially ferrous materialsprovided with a surface alloy of ferro chrome, which comprises firstforming a surface alloy on an object or base metal by cementation, andsubsequently heat treating, and working the same by a'metal formingoperation such as rolling, forging, swaging, drawing and the like.

Further objects and advantages of the invention will be apparent tothose skilled in the art to which it relates from the followingdescription thereof and the preferred method of practicing the same. 7

Surface alloys produced by cementation are not uniform in composition.In the extreme outer surface the cemented constituent is present inrelatively high concentration which tapers off to lower values towardthe interior. Upon being heated for several hours at a suitabletemperature and preferably in a suitable reducing or ert atmosphere, thecementation metal tends to migrate toward the interior of the material,the effect of which is to increase the thickness of the surface alloyproduced, but to dilute the content of the cementation metal at oradjacent the surface of the material. This is particularly true ofchromized ferrous material, and to various degrees is true of surfacealloys of other metals produced by cementation, such as surface alloy ofsilicon, boron, titanium, or tungsten produced on a foundation metal ofsteel or other ferrous materials. In each instance the surface alloy asproduced is relatively rich in the cementation metal at the outersurface with a gradual decrease in concentration thereof toward theinterior of the material, and subsequent heat treating under suitableconditions causes further migration of the cemented metal toward theinterior of the article with a reduction in the concentration thereof atthe outer surface.

I have found that ferrous metals which are first surface alloyed bycementation and then heat treated to reduce the concentration of thecementation metal at or adjacent the surface, as outlined above, can bereadily rolled or otherwise Worked at temperatures which are notparticularly critical, without cracking the surface alloy or making thesame porous, and under favorable circumstances, such material may becold rolled and otherwise cold Worked. The foregoing is particularlytrue of chromized steel and iron.

Briefly, the process of the present invention consists of producing on abase material a surface alloy by cementation in the usual manner, heattreating the same for a number of hours, anywhere from two hours up tofifteen or twenty hours, and even longer at temperatures anywhere fromabout 800 C. to those approximating the melting temperature of the basemetal, preferably about ten hours at from 1200 C. to 1350 C., to dilutethe concentration of the cementation metal at the surface and increasethe penetration thereof, and subsequently working the metal so treatedby either hot or cold metal forming operations to the desired shape.

As already stated, the present invention is particularly applicable toferrous materials provided with a surface alloy of ferro chrome producedby cementation, and the preferred practice of the invention will bedescribed in detail with reference to such materials. First a suitableiron or steel bar or billet is chromized, preferably by the processdisclosed in my copending application, Serial No. 75,237, or by theusual method. The chromized bar or billet is then heated in a neutralatmosphere, preferably hydrogen, for about 10 hours at from 1200 C. to1350 C., which will approximately double the thickness of the chromizedshell and correspondingly reduce the concentration of the chromiumadjacent the surface. Shorter heating an-d/ or lower temperatures lessenthe increase in thickness of the chromized shell and the dilution of thechromium at the surface. Conversely, longer heating at the highertemperatures increases the thickness of the chromized shell and thedilution of the chromium at the surfaces.

After theaforesaid heat treatment the bar or billet is rolled, forged,or otherwise worked at about the same temperature, preferably 1000 C.,or higher, and in much the same manner as ordinary steel or iron.Alternately, the bar or billet may be cold rolled or cold drawn. This isparticularly true of flat sections, where the reduction and distortionper pass is not excessive. The billets or bars may be readily reduced torods, wire, sheets, or other forms, and after being worked will have acontinuous surface of ferro chrome or other cemented alloy with a coreof simple steel or iron, as the case may be.

The phrase metal forming operation as used throughout the presentspecification and claims refers to such operations as forging, rolling,swaging, drawing, and the like.

Having thus described my invention, I claim:

1. The process of producing surface alloyed materials which comprisesforming a surface alloy of ferro chrome on a ferrous base metal bycementation, heat treating the same for a reasonable time at atemperature in excess of about 1100 C. to reduce the concentration ofthe chromium at the surface and increase the penetration thereof intothe base metal, and subsequently working the same to a desired shape bya metal forming operation.

2. The process of producing surface alloyed materials which comprisesforming a surface al- 10y of ferro chrome on a ferrous base metal bycementation, heat treating the same for a reason- 20 able time in excessof six hours at a temperature of about 1200 c. to 1350 C., andsubsequently working the same to a desired shape by a metal formingoperation.

3. The process of producing surface alloyed materials which comprisesforming the surface alloy of ferro chrome on a ferrous base metal bycementation, heat treating the same for a reasonable time in excess ofsix hours at a temperature of about 1200 C. to 1350 C., and subsequentlyworking the same to a desired shape by a hot metal forming operation.

4. The process of producing surface alloyed materials which comprisesforming a surface alloy of ferro chrome on a ferrous base metal bycementation, heat treating the same for a reasonable time in excess ofsix hours at a temperature of about 1200 C. to 1350 C., and subsequentlyworking the same to a desired shape by a cold metal forming operation.

HUGH S. COOPER.

